1. Field of the Invention
The present invention relates to a cooking stove wherein a cooking container is put on a trivet and heated and cooked by a burner.
2. Description of the Related Art
Conventionally, in the field of cooking stoves, a gas table 1 as shown in FIG. 15 and FIG. 16 has been known. In the gas table 1, a burner 14 of a spontaneous combustion type Bunsen burner is arranged at the center position of an opening arranged in a top plate 12, and a drip plate 18 is put around the burner. A cooking container P is put on a trivet 20 arranged above around the burner 14, and heated by combustion of the burner 14. Reference number 15 denotes a burner main body, and 16 denotes a burner head.
The trivet 20 is integrally structured of plural L-shaped trivet claws 22 onto which the cooking container P is put and a trivet ring 21 to be the base of the respective trivet claws 22, and is put on the top plate 12.
In the inner circumferential side of the trivet ring 21, an inclined jaw portion inclined downward to the center of the ring (hereinafter, simply referred to as jaw portion) 21c is formed.
Between this trivet ring 21 and the top plate 12, and between the trivet ring 21 and the drip plate 18, a clearance gap for supplying secondary air is formed.
Further, in recent years, as shown in the Japanese Patent Application Laid-Open No. 2003-161449, a cooking stove has been in practical use wherein the trivet claws 22 are made low and the clearance gap between the burner 14 and the cooking container P is made small for improving the heating efficiency of the cooking container P.
In this cooking stove, as shown in FIG. 17, the jaw portion 21c of the trivet 20 is extended to the vicinity of a main flame port 16a of the burner head 16, and secondary air is supplied to the base of the flame to the tip thereof.
The combustion gas of the burner 14 is discharged to the outside through the clearance gap (ring-shaped combustion gas route) between the cooking container P and the trivet ring 21. Reference number 23 donates a protruded portion that is inserted into the top plate 12 and supports the trivet ring 21.
By this structure, while the combustion performance is preferably maintained, the height of the trivet claws 22 is lowered to make the cooking container P close to the burner head 16, and the combustion gas of the burner 14 is prevented from diffusing by means of the trivet ring 21. Thus, the combustion gas at high temperatures contact with the cooking container P precisely, thereby increasing the heating efficiency of the cooking container P.
On the other hand, in this kind of cooking stoves, there are cooking stoves characterized by the structure of the trivet concerning improvement of thermal efficiency.
For example, as shown in Japanese Utility Model Application Laid-Open No. H02-140210, a trivet is proposed to have a spiral partition wall on the top surface of the trivet ring, and in the center position of the partition wall, a protrusion protruding upward is arranged as a kettle loading portion.
Further, in the Japanese Patent Application Laid-Open No. 2003-166718, a cooking stove is proposed. Wherein, a direction of a flame of an outer flame type burner is inclined by a specified angle in the burner circumferential direction to the straight line connecting the center of the burner and a flame port, and the a trivet is formed so as to be inclined in the same manner. Thus, a distance in which the flame contacts with the cooking container can be made long.
However, in the cooking stove as disclosed in the Japanese Patent Application Laid-Open No. 2003-161449, a high temperature combustion gas is prevented from diffusing by the trivet ring 21, and accordingly, the temperature of the trivet ring 21 becomes extremely high. As a result, the combustion gas heat is dissipated through the trivet ring 21, which has been a problem. In particular, in a cooking stove of forced combustion type where combustion air is forcibly supplied to the burner 14, and the combustion gas of the burner 14 is forcibly exhausted, it is possible to make the distance between the burner 14 and the cooking container P further shorter. However, since the high temperature combustion gas goes through on the surface of the trivet ring 21, the rate of the heat that is dissipated from the rear surface of the trivet 21 to the outside increases further more.
Further, in the case when the height of the trivet claws 22 is made low in this manner, it is possible to increase the contact area of the cooking container P and the combustion flame, but on the other hand, the contact area of the trivet claws 22 on which the cooking container P is put and the combustion flame increases further more.
Accordingly, as the flame is cooled down by the trivet claws 22 to deteriorate the combustion property, carbon monoxide gas generates, which has been another problem.
Furthermore, the heat energy of the flame is absorbed by the trivet claws 22, the heat transmission efficiency to the cooking container P declines.
Moreover, since the trivet claws 22 are heated up by the combustion flame, the durability of the trivet 20 is lost, and there is a fear of a burn injury to its user, which has been still another problem.
Further, in those conventional cooking stoves, although it has been considered to make the cooking container P close to the burner head 16, it was not considered to further improve the heating efficiency by the way to flow the combustion gas in the ring-shaped combustion gas route formed between the upper surface of the trivet ring and the bottom surface of the cooking container P, and there is room for improvement.
In general, the combustion gas (including the flame) generated by a burner is discharged through the ring shaped combustion gas route to the outside, and while the combustion gas passes through the route, its temperature goes down and its volume flow rate decreases. Further, since the ring shaped combustion gas route has a cross sectional area which increases toward the outside, the speed of the combustion gas in the combustion gas route becomes slower, so that the heat flow is dissipated toward the outside.
On the other hand, the heat transmission rate between the combustion gas and the cooking container becomes preferable when the combustion gas is passed through narrow ring shaped combustion gas route.
As a result, in the conventional cooking stoves, the heat flow is dissipated more at the outside in the ring shaped combustion gas route and sufficient heat exchange cannot be made.
On the other hand, in the cooking stove wherein a natural combustion type burner that supplies air necessary for combustion by natural draft force is used, if the distance between the bottom surface of the cooking container P and the burner 14 is made short, and the combustion space is made narrow, the draft force is not formed and the supply and discharge of combustion air cannot be made smoothly. Therefore, there is a limitation to make the combustion space narrow, which means that the distance between the burner 14 and the cooking container P becomes wide, so that the contact area of the combustion flame and the bottom surface of the cooking container P cannot be increased. Further, since the combustion space must be made wide, the combustion heat is dissipated unnecessarily in the combustion space, and the combustion heat is cooled down by ambient air flowing into the combustion space. Consequently, desired heating efficiency cannot be obtained.
Furthermore, even if the combustion gas flow is controlled so that the combustion gas is efficiently guided to the cooking container P for the purpose of improving the heating efficiency, it is difficult to control the combustion gas flow by only the natural draft force.
Accordingly, before the combustion heat is transmitted to the cooking container P sufficiently, the combustion gas is discharged to the outside, and there is a limitation in improvement of heating efficiency.
In the trivet of the Japanese Utility Model Application Laid-Open No. H02-140210, the cooking container is put on the protrusion arranged in the partition wall, the combustion gas route between the bottom surface of the cooking container and the trivet ring is not separated but interconnected at the upper portion. Therefore, the combustion gas (including the flame) of the burner does not circulate but just flows in the emission direction at the bottom surface of the cooking container.
Further, in the burner of the Japanese Patent Application Laid-Open No. 2003-166718, the jetting direction of the combustion gas is inclined and the trivet claws are formed so as to be inclined in the same direction. Accordingly, the combustion gas just flows diagonally to the emission direction, and the combustion gas does not sufficiently contact with the cooking container.
Namely, in any of these burners, the combustion gas flows under the cooking container in laminar flow state to the outside.
In this case, on the bottom surface of the cooking container, a heat transmission border film of a thin air layer is formed, and which works as a heat insulation layer. Thus, the heat transmission of the combustion gas to the cooking container has not been achieved.
As a result, it has been impossible to obtain high heating efficiency.
Accordingly, the object of the present invention is to solve the above problems with the prior art, and to eliminate energy loss arising from the trivet structure and the kinds of burners and obtain high heating efficiency.